Conifer growth stimulation and forest management

ABSTRACT

Conifer growth is stimulated by topical and/or foliar application of biuret which achieves direct contact of biuret with the conifer roots and/or foliage respectively. Foliar application is more effective on older trees. Optionally, undesired vegetation, such as ferns and broad-leaf plants, is controlled and conifer growth is promoted by application of biuret-containing solutions to the foliage of all plants. Novel compositions particularly useful in these methods contain biuret and a surfactant and/or polar solvent other than water sufficient to facilitate foliage wetting.

This application is a continuation of application Ser. No. 793,699,filed Oct. 31, 1985, and now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the field of conifer growth stimulation andforest management methods and compositions useful in such methods.

2. Description of the Art

Forest resource preservation and development becomes increasinglydifficult as societies become more industrialized and affluent. The moredeveloped the culture, the more destructive it becomes of its forestsdue to man-made calamities such as forest fires and to the consumptionof forest products such as lumber and pulp. Paradoxically, expanding,affluent populations also demand more recreational areas for enjoymentof increased leisure time. Unfortunately, these conflicting demandsoccur at a time when the choicest, most productive soils are employedfor agriculture or are occupied by industrial or residential structures.Consequently, silviculture is generally confined to remote areas inwhich soils are typically deficient in major and minor nutrientsrequired for abundant plant growth.

Efforts to improve forest growth and maximize productivity have involvedfertilization with either solid fertilizers or aqueous fertilizersolutions. Fertilization with solid nutrients usually involvesapplication of urea, ammonium nitrate or other nitrogen source asrelatively large solid prills of sufficient size to penetrate the forestcanopy and reach the ground surface. A majority of nitrogen applied inthis manner usually escapes by leaching or volatilization unless thenutrient is promptly washed into the soil and converted to nitrates (inthe case of urea). Consequently, such practice is usually employed onlyduring the rainy season and, thus, is logistically inefficient due tothe intensity of effort required for wide spread fertilization in thefew rainy months. Such practice also causes maximum ecologicaldisruption since the fertilizer is applied at the time when it is mostlikely to contaminate forest streams and lakes. The use of solidfertilizer in this manner is inefficient for the further reason thatmuch of the applied nitrogen is rapidly assimilated by shallow-rootedundergrowth such as ferns and broadleaf vegetation. More efficientfoliar fertilization methods are described in my U.S. Pat. No. 4,033,747for Silvicultural Fertilization and involve the application ofconcentrated nitrogen solutions directly to the forest canopy.

The presence of undesired vegetation such as ferns, weeds, and broadleaftrees and plants further complicates conifer forest management even inthe absence of fertilization since such plants compete with conifertrees for nutrients and impair access to forested areas. Competition fornutrients, sunlight and water is particularly detrimental to conifergrowth in reforested areas since broadleaf trees and underbrushtypically grow much faster in their earlier stages of development thando conifer seedlings. Thus, broadleaf plants and other undergrowth cancompletely crowd out small conifer seedlings or markedly impair theirgrowth rate unless the non-conifer species are controlled by mechanicalor chemical thinning. One method for simultaneously fertilizing conifersand eliminating competing non-conifer growth is disclosed in U.S. Pat.No. 4,035,173 of S. Hashimoto and Donald C. Young, Selectively Thinningand Fertilizing Timber Forests, the disclosure of which is incorporatedherein by reference in its entirety. That patent teaches, in part, thatbroadleaf plants can be selectively eliminated from preferred conifertrees by applying to the foliage of all plants an aqueous solution of awater-soluble nitrogen source having a nitrogen concentrationcorresponding to at least about 12.5 weight percent elemental nitrogenat a nitrogen dosage rate sufficient to kill a significant proportion ofthe broadleaf plants. Other chemical thinning methods usually involveherbicide application by ground personnel or vehicles, both of which aretedious, time consuming and expensive, as is mechanical thinning byground personnel. Yet such procedures are sufficiently productive tojustify their use. Mechanical clearing of undesired vegetation issometimes practiced even as late as 15 years after planting andtypically involves substantial costs on the order of $100.00 to morethan $500.00 per acre. Yet the United States Forest Service hasestablished that ultimate wood protection can be increased sufficientlyto justify such practices.

Biuret is known to be highly phytotoxic to essentially all plantvarieties when applied in a manner which provides direct contact witheither plant foliage or roots. Biuret applied to the soil of deep rootedplants is generally less toxic since it is only slightly soluble inwater (less than 2 weight percent at 25° C.) and is generally degradedin the soil before it can be assimilated by the plant. However,application of biuret directly to plant foliage or to shallow rootedplants, such as young seedlings, is known to produce dramatic phytotoxicresponse and often results in plant stunting or death. Many authoritiesflatly state that the biuret content of foliarly applied urea should notexceed 0.25 weight percent. See, for instance, the "Farm ChemicalsHandbook," Meister Publishing Company., Willoughby, Ohio, 1981 under"Urea" and "LB Urea", and the "Western Fertilizer Handbook", 5th. Ed.Interstate Printers and Publishers, Inc., Danville, Ill., 1972, page163. Paradoxically, biuret is often formed during the manufacture ofurea, especially prilled urea--one of the most widely used nitrogenfertilizers. For that reason, various safeguards are built into modernurea manufacturing facilities to prevent biuret production, and variousprocedures have been devised for removing biuret from urea. Illustrativebiuret-removal methods are discussed by Donald C. Young and James A.Green, II in Ser. No. 753,692 filed July 10, 1985 for Methods forRemoving Biuret from Urea by Adsorption, now U.S. Pat. No. 4,701,555,Ser. No. 753,693 filed July 10, 1985 for Biuret Purification, now U.S.Pat. No. 4,698,443, Ser. No. 732,175 filed May 7, 1985 for BiuretManufacture, now U.S. Pat. No. 4,645,860, Ser. No. 725,304 filed Apr.19, 1985 for Methods for Purifying Biuret, now U.S. Pat. No. 4,645,859,Ser. No. 567,271 filed Dec. 30, 1983 for Methods for Removing Biuretfrom Urea by Ion Exchange, now U.S. Pat. No. 4,658,059, Ser. No. 567,099filed Dec. 30, 1983 for Ion Exchange Methods for Removing Biuret fromUrea, now U.S. Pat. No. 4,650,901 and Ser. No. 567,047, filed Dec. 30,1983 for Methods for Removing Biuret from Urea, now U.S. Pat. No.4,654,442 the disclosures of which are incorporated herein by referencein their entireties.

SUMMARY OF THE INVENTION

It has now been found that biuret is not phytotoxic to conifers even atvery high per acre dosage rates, that biuret can be employed as both atopical and foliar fertilizer for conifers even in the absence of othernutrients, and that biuret applied directly to conifer foliage or rootsat relatively low dosages increases growth by an amount greater than canbe accounted for by increased nitrogen availability. Higher biuretdosage rates further increase conifer growth and can be employed toeliminate competing forest vegetation which is susceptible to biuretphytotoxicity. Significantly increased growth rate has been observed inredwood seedlings (Sequoia sempervirens) at dosage rates as high as2,000 pounds of biuret per acre without any evidence of phytotoxicity.Novel compositions useful in these methods contain biuret and one ormore surfactants or polar solvents other than water in the presence orabsence of other components.

The methods and compositions of this invention increase conifer growtheven at very low biuret dosage rates and, therefore, can be used toincrease conifer growth with only minor nitrogen addition to theenviroment. Such practice is advantageous particularly in areas whichalready have adequate nitrogen availability. They can be employed toincrease conifer growth even further by the addition of nitrogen sourcesother than biuret such as urea, ammonium nitrate, etc., and they can beused to eliminate competing non-conifer vegetation such as ferns andbroadleaf trees and brush and thereby benefit conifer growth (due to thelack of competing varieties) and facilitate access to forested areas.The useful biuret-containing compositions cause less nitrogen runoffinto streams and lakes due to biuret's low solubility, and they resultin less loss, and therefore more efficient use, of nitrogen Biuret'simmunity to enzymatic action and volatilization (in contrast to urea)improves the efficiency of these methods and compositions even further.

DETAILED DESCRIPTION OF THE INVENTION

Conifers which can be treated with the described methods andcompositions include all members of the order Coniferales of evergreentrees and shrubs. Timber trees are of greatest commercial significanceand are generally selected from the family Pinaceae, commonly known asthe "pine" family, which includes several genera, each of whichencompasses numerous species. The generic classes within the pine familywhich constitute the principal commercial timber and wood by-productcrops are the Abies, including all of the true firs such as Pony fir,Grand fir, Red fir, etc.; Picea, including numerous species of spruce;Pinus, including many species of pine such as loblolly, ponderosa,lodgepole, white pine, etc.; Pseudotsuga or false hemlock, the Douglasfir being a member of this genus rather than a true fir; Tsuga,including numerous species of hemlock; and Sequoia, including thespecies sempervirens and gigantia. The remaining two pine family genra,while generally being of lesser commercial importance within the contextof this invention, are still suitable subjects for treatment with thedescribed methods and compositions. Those include the genus Cedrusincluding all species of cedar and the genus Larix including thetamaracks.

The described methods and compositions can be employed to eliminate andcontrol a wide variety of non-coniferous forest vegetation such as fernsand broadleaf trees, brush and vines. Illustrative broadleaf varietiesare the Maple genus including numerous species of maples, the Birchgenus including the common birch and alders, the genus Populus includingpoplars, and the Beech genus including numerous varieties of oaks andother species. Low lying broadleafs include numerous varieties of weeds,vines, and bushes such as ferns, i.e., the class Filicineae, running orclimbing vines such as wild grapes, so-called arrowroot plants of thegenus Maranto, wild flowering plants such as thistles and goldenrod andthe numerous wild shrubs generally referred to as brush andcharacterized as woody plants having several permanent stems rather thana single trunk.

The compositions useful in these methods contain sufficient biuret topromote the growth of conifers, and, optionally, they contain sufficientbiuret to inhibit the growth of non-coniferous plants growing in thetreated vicinity. Such compositions can be either solid or liquid,although liquid compositions are particularly preferred, as is foliarapplication. Solid compositions can be applied to relatively youngtrees, i.e. trees 5 or less, generally 3 or less years old, andparticularly potted seedlings which have shallow root systems thatenable direct contact of the root system with biuret applied to thesoil. Soil-applied biuret can be washed into the root zone of suchshallow-rooted plants before it is decomposed by soil bacteria.

Typically, the biuret concentration will be sufficient to account for atleast about 0.5, generally at least about 1 and preferably at leastabout 2 percent of the total nitrogen present in the composition. Higherbiuret concentrations are preferred when lower total nitrogen dosagerates are required, as is the case when nitrogen availability is alreadysufficient to support adequate growth. In such instances, the biuretconcentration will correspond to at least about 5, preferably 10 toabout 100, and most preferably 20 to about 100 percent of the totalnitrogen present in the composition. Most often, biuret concentrationwill account for about 2 to about 100 percent of total nitrogen.

The useful liquid compositions (as applied either to the ground orfoliage) will contain about 0.05, generally at least about 0.1, andpreferably at least about 1 weight percent biuret dissolved insufficient liquid (water or other solvent) to enable adequatedistribution. Typically biuret concentrations in the useful liquids willbe from about 0.1 weight percent to the biuret solubility limit underapplication conditions. Biuret is more soluble in urea solutions, andits solubility increases as temperature is increased. Thus, higherbiuret concentrations can be achieved by employing relativelyconcentrated urea solutions, i.e. solutions containing 10 to 60 weightpercent urea, and elevated temperatures, i.e. up to about 60° C. Theuseful solid compositions usually contain about 1 to about 100 weightpercent biuret.

The liquid compositions are preferably aqueous solutions or dispersionsalthough other non-aqueous polar solvents or combinations of water andsuch solvents can also be employed. Such solutions and dispersions arepreferably sufficiently concentrated to enable delivery of the desiredbiuret dosage rate without runoff from plant foliage. Typicalapplication rates correspond to about 200 gallons per acre or less.

Biuret dispersions are especially useful for applying high biuret dosagerates in limited quantities of liquid, particularly in the absence ofcomponents, such as urea, which increase biuret solubility. Typically,such dispersions contain about 5 to about 75 weight percent finelydivided (e.g., minus 100 mesh) biuret, about 0.5 to about 10 weightpercent suspending agent, and about 0.25 to about 2 weight percentsurfactant. Illustrative surfactants are defined herein after.Illustrative suspending agents are clays such as bentonite andkieselguhr, and natural and synthetic water-soluble polymers such ascarboxymethylcellulose, polyamides, alganates, etc.

Conifer growth rate can be increased even more by the addition of othernitrogen sources such as urea, ammonium nitrate, ammonium phosphate,ammonium sulfate, etc. Thus, when it is not necessary to limit totalnitrogen dosage, the applied liquids preferably contain at least about5, generally at least about 10 and most preferably about 30 weightpercent total nitrogen dissolved in a suitable solvent, preferablywater. Suitable nitrogen-containing solutions are discussed in moredetail in my U.S. Pat. No. 4,033,747 the disclosure of which isincorporated herein by reference in its entirety.

The useful solid compositions can consist essentially of biuret or canbe mixtures of biuret and other nitrogen sources or fillers such asclay. Such compositions are preferably applied to forest areas in theform of prills of sufficient size to penetrate the forest canopy.However, they can also be applied to the foliage or soil surface aspowders which adhere to the foliage and enter the plant due to theaccumulation of moisture and dissolution of biuret on the foliagesurface.

The novel solid and liquid compositions contain sufficient biuret topromote conifer growth, and optionally, inhibit the growth ofnon-coniferous plants, and one or more surfactants and/or polar solventsother than water. The biuret usually accounts for at least about 2,preferably at least about 5 and most preferably about 10 to about 100percent of the total nitrogen contained in the composition. The mostpreferred compositions are aqueous solutions of urea and biuret in whichthe biuret/urea weight ratio is at least about 0.02, preferably at leastabout 0.05 and most preferably at least about 0.1. The higherbiuret/urea weight ratios are particularly preferred when low totalnitrogen dosage rates are required.

The surfactants and polar solvents other than water facilitate foliagewetting and solution distribution and thereby promote rapid assimilationof biuret (and other dissolved components if present) by both conifersand non-coniferous plants. Relatively minor surfactant concentrationsare usually sufficient and correspond to at least about 0.1 weightpercent, generally about 0.1 to about 2.5 weight percent, and typicallyabout 0.25 to about 1 weight percent. Similar or higher concentrationsof polar solvents other than water can be employed. Thus, the biuret(and other components when present) can be dissolved in water containing0.5 weight percent of a polar solvent other than water, or the solventcan consist essentially of a non-aqueous polar material such asaldehydes such as formaldehyde, propionaldehyde, etc., ketones such asmethylethylketone, alcohols such as isopropanol, organic acids such asacetic, butyric, propionic, etc., amines, amides, thiols, and otherpolar compounds and combinations of such compounds. A variety ofsurfactants is useful in this embodiment, including cationic, anionicand nonionic surfactants and combinations of these. Illustrative classesof suitable surfactants are fatty amines, alkarylamines, fatty amides,quaternary alkyl and aryl ammonium salts and hydrates, quaternaryammonium bases of fatty amines and disubstituted diamines, fatty acidsulfonates, sulfonated fatty amides, amides of amino sulfonic acids,alkylaryl sulfonates and the like. Illustrative nonionic surfactantsinclude poly-ethylene oxide condensates with hydrophobic groups havingreactive hydrogens. These hydrophobic groups can have from about 8 toabout 25 carbons and from about 2 to 15 molecular weights of thehydrophilic group. The hydrophobic groups can be selected from a varietyof organic compounds having 1 or more reactive hydrogens including fattyalkyl or alkenyl alcohols, fatty acids, amines and amides, esterifiedhexitans or alkenyl phenols. The hydrophilic groups can be ethyleneoxide moieties or groups such as ethylene chlorohydrin or polyethyleneglycol. Still other illustrative surfactants include the organicsubstituted ammonium salts of sulfodicarboxylic acids that are reactedwith various hydrophobic groups such as fatty amides having 12 to 18carbon atoms to produce half amides in the manner described in U.S. Pat.No. 2,976,209 the disclosure of which is incorporated herein in itsentirety. Other materials of this type are described in U.S. Pat. Nos.2,976,211, 3,080,280 and 2,976,208, the disclosures of which areincorporated herein by reference in their entireties. The solid andliquid compositions may also contain other ingredients such asmacronutrients, micronutrients, insecticides, fungicides and/orherbicides which are selective toward non-coniferous vegetation and arenot significantly phytotoxic to conifers.

The liquid compositions can be obtained by dissolving biuret and othercomponents, if present, in water or other solvent. Surfactants, polarsolvents other than water, nutrients, herbicides, insecticides, etc.,can be added in any order of mixing. Biuret can be obtained by any oneof a variety of procedures including pyrolysis and selectivecrystallization as disclosed by Shipley and Watchorn in British PatentNo. 1,156,099 and by Kaasenbrood in U.S. Pat. No. 3,185,731 thedisclosures of which are incorporated herein in their entireties.Particularly useful methods for obtaining biuret from urea are disclosedby James A. Green, II and Donald C. Young in above-referenced copendingapplications Ser. No. 725,304, now U.S. Pat. No. 4,645,859, Ser. No.732,175, now U.S. Pat. No. 4,645,860, and Ser. No. 753,693, now U.S.Pat. No. 4,698,443.

Conifer growth can be stimulated by contacting the foliage or roots ofconifers with one or more of the described solid or liquidbiuret-containing compositions at a biuret dosage rate sufficient topromote conifer growth. Very minor biuret dosage rates on the order of0.05 pounds per acre produce a beneficial effect. However, higher biuretdosage rates usually produce greater growth enhancement and aretherefore preferred. Thus, biuret dosage rates are usually at leastabout 0.1, preferably at least about 1 and most preferably at leastabout 10 pounds of biuret per acre. Even higher biuret dosages, i.e. 20pounds per acre and more, increase conifer growth even further. Redwoodseedlings approximately 6 inches high were treated with biuret at adosage rate corresponding to 2,000 pounds of biuret per acre appliedtopically without any detectable phytotoxic effect. As a general rule,biuret dosage rates will be within the range of about 1 to about 5,000pounds of biuret per acre.

In addition to the paradoxical nutrient effect of biuret on conifers, ithas further been observed that the growth enhancement realized by biuretapplications at relatively low dosage rates, i.e. 0.1 to about 2 poundsper acre, exceeds the growth enhancement observed by application ofother nitrogen fertilizers at identical nitrogen dosage rates by afactor of 2 or more. Thus, threshold quantities of biuret enhanceconifer growth to an extent which cannot be explained on the basis ofnitrogen content alone. Without intending to be constrained to anyparticular theory or mechanism of operation, it presently appears thatsuch threshold quantities of biuret behave as plant growth regulants atleast to the extent that they promote conifer growth by an amount fargreater than that attributable to nitrogen contribution per se. Thisappears to be particularly true when the biuret is foliarly applied,especially on mature conifers, e.g. 5 years old or more.

Since the biuret must be contacted with the plant foliage or roots inorder to exhibit its maximum growth potentiating effect, the topicalapplication of the solid compositions is usually effective only onshallow rooted trees which are about 5 years old or less, preferablyabout 3 years old or less. Topical application to seedlings about 2years old or less has demonstrated significant growth increase with onlyminor biuret dosage rates. Application of the powdered compositions toplant foliage is effective provided that sufficient moisture isavailable in the atmosphere for absorption by the powder to dissolvebiuret which then penetrates the plant foliage. Otherwise, foliarapplication of the liquid compositions is preferred, and suchcompositions can be applied at any growth stage of the treated conifers.

Selective elimination of competing non-coniferous growth is preferablyaccomplished by foliar application of the useful solutions at biuretdosage rates sufficient to completely eliminate such vegetation. Whileany significant control of undesired vegetation has a beneficial effecton the conifer crop, the biuret dosage rates typically are sufficient toeliminate at least about 50 percent, preferably at least about 70percent of the non-coniferous vegetation. Biuret dosages sufficient toeliminate a significant proportion of competing vegetation will usuallybe at least about 1, generally at least about 5, preferably at leastabout 10, and most preferably at least about 20 pounds of biuret peracre.

It is sometimes desirable to eliminate non-coniferous species (or atleast retard the growth of a significant portion of such species)without adding significant amounts of nitrogen to the envirorment. Thisis particularly true when nitrogen is already in plentiful supply. Insuch instances, the biuret will constitute at least about 5, generallyat least about 10 and preferably at least about 20 percent of the totalapplied nitrogen. As a general rule, selective elimination ofnon-coniferous species is achieved by the use of compositions in whichbiuret constitutes about 5 to 100 percent of the applied nitrogen.Compositions in which biuret constitutes 10 to 100 percent of availablenitrogen are particularly desirable for areas of high nitrogenavailability. The described novel compositions which contain one or moresurfactants and/or polar solvents other than water are particularlypreferred for the selective elimination of non-coniferous plants.

The solutions can be applied by hand spraying or mechanical sprayingfrom land vehicles or can be aerially applied by helicopter or otheraircraft. The amount of solution applied will generally be determined bythe desired solution concentration and the total dosage level. Theseapplication rates usually correspond to about 15 to about 200,preferably about 25 to about 100 gallons of solution per acre. A secondconsideration involves the amount of solution required to sufficientlycover the foliage and distribute the compounds without substantialdrainage from the foliage to the forest floor. Such drainage ispreferably avoided since less benefit is achieved by applying the usefulcompositions to the forest floor, especially in mature forests, and suchapplication may result in contamination of ground water and adjacentrivers and streams.

The compositions are preferably applied annually, although more frequentapplications such as semi-annual or quarterly treatments can be used.Applications are preferably made shortly before or during the activegrowing season, e.g., in the early or late spring, so that the greatestgrowth advantage is achieved. Similarly, non-conifers, e.g. broadleafs,are more effectively inhibited during the active growing season due tothe higher foliage levels during that period.

The invention is further described by the following examples which areillustrative of specific modes of practicing the invention and are notintended as limiting the scope of the invention as defined by theappended claims.

EXAMPLE 1

Approximately 2.5 kg. of Tumwater fine sandy loam (pH 5.5) were placedin each of 384 2.5-liter plastic pots. Following random assignment toeither Douglas-fir or western hemlock, each pot was sown in early Maywith 10 previously stratified seeds of the assigned species. The potswere kept in a greenhouse where extremes of soil temperature weremoderated by surrounding the pots with peat moss that was periodicallymoistened. Soil within the pots was maintained near field capacity byperiodic watering. Approximately 16 hours of light per day were providedby seasonally using artificial light. Greenhouse temperatures weremaintained between 10° and 32° C. Three months after sowing, allseedlings were thinned to 5 per pot to achieve uniform spacing andheight; then 24 different treatments were randomly assigned to differentpots of each species. Ther were 8 replicates of each test.

The 24 fertilizer treatments on each species were arranged as a 4×2×3factorial testing 4 levels of biuret (0, 0.224, 2.24, and 22.4 kg.ha⁻¹), 2 methods of application (biuret applied as solution to eitherthe soil or sprayed on the foliage), and 3 levels of nitrogen (0, 84 or168 kg. ha⁻¹ as urea). The 48 treatment × species combinations wereinitially replicated eight times. All solutions were prepared fromreagent-grade urea or biuret and were first applied when the 2-month oldDouglas-fir were 2 to 6 cm. tall and the hemlock were 1 to 2 cm. tall.

After the first growing season, four of the 8 replicates were randomlyselected for harvest and designated as Example 1. The remainingreplicates were designated as Example 2 reported below.

Oven-dry weights of all harvested roots, tops and the combination ofthese were determined by drying to constant weight at 105° C. Averageseedling weight per pot was determined on the basis of the number ofsurviving seedlings per pot; i.e. 5 for almost all pots. The resultswere analyzed for variance using orthogonal polynomials to establishregressions for average seedling weight per pot versus total nitrogen orbiuret dosage. These results established that total seedling weightincreased linearly with biuret dosage for all treatments up to a maximumof 14 percent gain for the biuret-treated seedlings compared tobiuret-free treatments. In this experiment, topical biuret applicationconsistently produced more weight gain than did foliar application.However, the comparison of topical and foliar application in thisexperiment was complicated by solution runoff in foliar applications,the very shallow roots of small seedlings and the high permeability ofthe test soil. All of these factors may have combined to provide adegree of direct biuret contact with seedling roots far greater thanthat which could occur with topical application in a normal forestsituation.

Comparison of total weight gains for all treatments and both treespecies established that biuret was from 2 to 1,110 times more effectivethan urea as a nitrogen source depending on tree species and treatment.In other words, the total weight gain observed as a result ofbiuret-nitrogen application ranged from 2 to 1,110 times greater thanthat which occurred as a result of urea-nitrogen application based oneach unit of applied nitrogen.

EXAMPLE 2

The four replicates of each test in Example 1 which were not harvestedin that example were rethinned to leave three seedlings per pot and wereretreated with biuret, urea or a combination of these, before the secondgrowing season. Retreatments in each pot corresponded to the originaltreatment for that pot. Thus, the experimental design of this examplewas the same as in Example 1. Seedlings of this example were tendedduring the second growing season as described in Example 1.

At the end of the second growing season, all plants were harvested andevaluated as described in Example 1. Total weight increased linearlywith biuret dosage for all treatments. The maximum weight gain for thebiuret treatments was 14 percent higher (total dry weight) than for thebiuret-free treatments. Expressed in terms of nitrogen efficiency,biuret produced about 2 to 310 times the total weight gain per nitrogendose as did biuret-free urea depending on tree species and urea-biuretdose. In other words, the total weight gain associated with nitrogendose ranged from 2 to 310 times higher for biuret-nitrogen than forurea-nitrogen even though urea significantly increased seedling totaldry weight.

While particular embodiments of this invention have been described, itwill be understood, of course, that the invention is not limited theretosince many obvious modifications can be made, and it is intended toinclude within this invention any such modifications as will fall withinthe spirit and scope of the appended claims.

I claim:
 1. A method for promoting the growth of conifers whichcomprises applying to said conifers an amount of biuret sufficient topromote the growth of said conifers.
 2. The method defined in claim 1wherein said biuret is applied to the foliage of said conifers.
 3. Themethod defined in claim 1 wherein said biuret is applied to the foliageof said conifers as a liquid solution or dispersion.
 4. The methoddefined in claim 1 wherein said biuret is applied to said conifers as anaqueous solution comprising a member selected from the group consistingof surfactants, polar solvents other than water, and combinationsthereof.
 5. The method defined in claim 1 wherein said biuret is appliedto said conifers at a rate corresponding to at least about 0.1 pound ofbiuret per acre.
 6. The method defined in claim 1 wherein said biuret isapplied to said conifers at a rate corresponding to at least about 1pound of biuret per acre.
 7. The method defined in claim 1 wherein saidbiuret is applied to said conifers at a rate corresponding to at leastabout 10 pounds of biuret per acre.
 8. The method defined in claim 1wherein said biuret is applied to said conifers in a compositioncomprising a plant nutrient in addition to said biuret.
 9. The methoddefined in claim 1 wherein said biuret is applied to said conifers in acomposition further comprising a compound selected from the groupconsisting of urea, ammonium and potassium sulfates, nitrates,phosphates, and combinations thereof.
 10. The method defined in claim 1wherein said biuret is applied to said conifers in a composition whichfurther comprises urea.
 11. The method defined in claim 1 wherein saidbiuret is applied to said conifers in a composition which furthercomprises urea, and the biuret/urea weight ratio is at least about 0.02.12. The method defined in claim 1 wherein said biuret is applied to saidconifers in a composition which further comprises urea, and thebiuret/urea weight ratio is at least about 0.05.
 13. The method definedin claim 1 wherein said biuret is applied to said conifers in acomposition which further comprises urea, and the biuret/urea weightratio is at least about 0.1.
 14. The method defined in claim 1 whereinsaid biuret is applied to said conifers at a rate corresponding to about0.1 to about 20 pounds per acre, and said conifers are about five yearsold or less.
 15. The method defined in claim 1 wherein said coniferscomprise commercial timber trees of the family Pinaceae.
 16. The methoddefined in claim 1 wherein said conifers comprise trees selected fromthe group consisting of the genra Abies, Sequoia, Picea, Pinus,Pseudotsuga, Tsuga, and combinations thereof.
 17. The method of claim 1wherein said conifers are selected from the group consisting of Grandfir, Red fir, Pony fir, hemlock, spruce, cedar, loblolly pine, Ponderosapine, lodgepole pine, white pine, sequoia sempervirens, and combinationsthereof.
 18. The method defined in claim 1 wherein said biuret isapplied to the foliage of said conifers as an aqueous solution in whichthe biuret/urea weight ratio is at least about
 1. 19. The method definedin claim 1 wherein said biuret is applied to the foliage of saidconifers as an aqueous solution comprising at least about 5 weightpercent urea in which the biuret/urea weight ratio is at least 0.05. 20.The method defined in claim 1 wherein said conifers are growing in thepresence of non-coniferous plants, and said biuret is foliarly appliedto said conifers and said non-coniferous plants at a dosage ratesufficient to inhibit the growth of said non-coniferous plants.